Aligning circuit features that are created in different stages of the production process is a major challenge in the manufacturing of printed circuit boards. In a typical process, the circuit panel is first drilled to create through-holes; then layers of copper conductors, including pads and interconnections, are deposited on the panel; and finally a solder mask is overlaid on the conductors in preparation for assembling the circuit. (This sort of process is described, for example, by Michael Flat in “Printed Circuit Board Basics,” third edition, Miller Freeman Books, ISBN 0-89730-486-3, 1997.) Incorrect alignment of any of these elements (holes, conductors or solder mask) may lead to faults in the circuit.
Various methods are known in the art for aligning circuit elements in the successive stages of production. For example, U.S. Patent Application Publication 2005/0213806, whose disclosure is incorporated herein by reference, describes a system and method for manufacturing printed circuit boards using non-uniformly modified images. An initial version of a computerized image of a pattern is supplied to a recording system, such as a laser direct imaging system, which modifies the initial version of the image non-uniformly prior to recording the modified version of the pattern on a substrate. The dimensions and/or shape of the pattern are modified so as to correspond to an electrical circuit pattern that was previously recorded on the substrate.